Several devices have been published that measure the anterior-lateral rotational instability of the knee but they are lacking a number of important simulations of the human knee. In a paper entitled "Stiffness and Laxity of the Knee--Contributions of the Supporting Structures" by Markolf et al. which appeared in the July 1976 issue of the Journal of Bone and Joint Surgery, pages 583-604, apparatus for testing various aspects of the knee are disclosed but the data there obtained can be in error because there was no "body weight" or quadriceps force applied so actual knee loading was not reflected in the data. In a paper by Wang et al. entitled "Rotary Laxity of the Human Knee Joint" which also appeared in the Journal of Bone and Joint Surgery", January 1974, page 161-170, a knee apparatus was disclosed which utilized a rotary laxity rig and an automatic. Instron loading machine in which tibial and femural bone fixtures grasp the bone and various rotary and loading forces were applied on the knee joint. Again, there was no actual body weight or quadriceps knee loading. Finally, in an article co-authored by the inventor hereof entitled "The Role of Incompetence of the Anterior Cruciate and Lateral Ligaments in Anterolateral and Anteromedial Instability", by Lipke et al, published in the July 1981 issue of the Journal of Bone and Joint Surgery", pages 954-959, a knee loading and testing apparatus is disclosed wherein a gravity load on the knee is simulated by an air cylinder articulating a mounting for the tibia bone while maintaining stationary the mounting for the femur bone and clamping the quadricep muscle ligament. The fibula bone is left free. That publication is believed to disclose the most pertinent art relative to the present invention.
According to the present invention, the quadricep length is variably controlled to allow variation in the torque and pull and at the same time, both the femur and tibia mountings are independently articulatable, and further, these various loadings may be controlled and recorded by a computer and the response of the joint to various loadings may be recorded for future study and analysis by any computer.
As compared with the disclosures in the above Lipke et al article, the present invention provides for release of both the transverse and coronal plane drives while still measuring angulation. Thus, the present invention provides a releasable drive to the mountings for the femur and tibia so that data may be obtained under a wider variety of simulated loading conditions than heretofore. While the invention has been developed for use in conjunction with cadaver knee joints, it is believed that several modifications of the invention can be applied to live knee joints for in vivos study, particularly of knees having sustained damage as for example an athlete such as a basketball or football player. A closed loop control (servo control) is also provided.
In the device disclosed in the above Lipke et al article, flexion angle is measured two ways, (1) a three plane goniometer as disclosed in my U.S. Pat. No. 4,306,571 is attached to the test fixture or, (2) it is measured at the hip (femur flexion) and the measured value doubled. According to the present invention, the femural flexion and the tibial flexion are independently measured and then they are summed. This is a more accurate way of measurement as it takes into account for differences in the length of the femur and tibia bones.
Only two of nine test variables associated with testing could be measured in the machine disclosed in the Lipke et al article whereas in the present machine, all nine variables can be measured and recorded in nine separate data channels simultaneously. In the machine disclosed in the Lipke et al article, if more than two parameters were required to be compared for a given knee, the knee had to be re-tested, hopefully under the same conditions for each test. In the present invention, one test can provide comparison between any of the parameters in any combination. Hence, the present invention provides a knee testing apparatus which is more accurate and far more flexible than that disclosed in the Lipke article.
In the machine disclosed in the Lipke article, there were no limits as to the magnitude of an input except as determined by the aptitude of the operator. And, with the unknown quality of cadaver knees being tested, the operator could be subjected to serious injury should some component of the knee joint being tested fail. The present invention provides pre-set limits on quadricep force and body weight that can be applied. If either of these are exceeded, the machine provides an acoustic annunciator to advise the operator of an overload, and at the same time, disable the controls which would further increase these load functions. Only the control for decreasing these functions remain operable and the annunciator remains active until the overload is eliminated.
The hip assembly apparatus of the present invention permits the use of attachments for providing "ham string" muscle group simulations without modification of the hip assembly. In addition, the present invention provides measurement of the anterior/posterior force and distance of the tibia with respect to the femur without modification. Furthermore, the present invention provides for locking the hip against rotation in the sagittal plane at any position in its usable range, and, finally, according to the present invention, the vertical motion of the ankle assembly may be locked at any point in the offset range of the ankle.
Advantages of the invention include the following:
the invention provides the knee under test to be stabilized by its own geometry which enhances accuracy of measurement;
has the capability of releasing the drives for either the transverse or coronal plane motions while still measuring the angulation of the tibia in both planes;
has the advantage of releasing both the transvere and coronal plane drives at the same time while still measuring angulation in both planes;
thus, in view of these advantages, the invention can measure in one test, the "screw home" motion of a knee, thus providing a natural test bed for comparisons of "normal" knees and prosthetic implant;
the invention permits anterior/posterior measurement of tibial force and distance with respect to the femur on loaded or unloaded joints;
remote master/slave hydraulic quadricep force mechanisms can easily be connected to hydraulic closed loop control;
all controls are designed to permit simple conversion to closed loop control (servo control) using either the existing computer in the loop or a different one;
since the data is handled by a computer the results of the test may be presented in either English, metric or S1 (Systems International) units as may be desired by the operator;
the data is stored in such manner that the polynominal curve fitting software is included on the control disk (the control software) and can sample and curve fit any pair of data sets of the nine channels stored.
Furthermore, the invention provides accurate testing and teaching of surgical/reconstruction techniques because it permits the knee to be its own standard for before and after surgery on the specimen. Since, in the present invention, the knee specimen can be rotated about an axis through the hip and ankle, viewing, surgical procedures and x-raying may be performed with the specimen in place thus eliminating removal/installation errors from the data. During the data taking sequence, the invention measures and stores all nine data channels in approximately 600 microseconds, thus assuring that there is no significant time change or phase shift from the first to last measurement. Finally, since the machine uses "quad force" applied through the patella and permits simulation of abnormal patello-femural interaction by providing for a wide range (plus or minus 20 degrees) of "Q" angle variation, injuries, diseases and abnormalities associated with this articular surface can be studied (the Q angle is the angle between the direction of quad force pull and the center line of the femural shaft and the medial/lateral direction).